The present invention relates to an electrophotographic copying apparatus and more particularly, to an electrophotographic copying apparatus having a transparent platform, for example, of glass material disposed at an upper portion of the copying apparatus for supporting a thick original such as a book to be copied on said transparent platform, and a transporting means for a thin original such as a sheet of paper (referred to as sheet original hereinbelow) provided with transportation rollers and disposed adjacent to the transparent platform so that during copying of a thick original, the image forming optical system scans the original from beneath the transparent platform for sequentially exposing a photosensitive member or photoreceptor to image-carrying light from the original, while for copying a thin sheet original, the thin sheet original is transported by the sheet original transporting means, with the image forming optical system remains stationary, for sequentially directing the image-carrying light from the sheet original onto the photoreceptor for exposure.
Conventionally, in the electrophotographic copying apparatus of the above described type, there has been proposed, for example, in U.S. Pat. No. 3,947,111 issued Mar. 30, 1976, an arrangement in which a thick original is placed on a transparent platform of glass material for copying of such a thick original, and an image forming optical system is moved under the transparent platform for sequential scanning so as to expose a photosensitive member to light images of the thick original, while for the copying of a thin original in sheet form, a sheet original transporting means having transportation rollers is adapted to move onto the transparent platform, with the image forming optical system being kept stationary after having been moved to a predetermined position below the sheet original transporting means, the sheet original transporting means transporting the sheet original for sequentially exposing the photosensitive member to the light images from said sheet original.
The known copying apparatus as described above, however, has various disadvantages in that, for copying the sheet originals, the sheet original transporting means must be moved onto the transparent platform after a pressing cover for the original which is hingedly mounted on the platform has been raised upward to an opened position, thus requiring a troublesome procedure, and moreover, since the transportation rollers engage only on the upper surface of the sheet original to be transported, there is a tendency for a sheet original of comparatively small stiffness not to be positively transported but rather to be subject to wrinkling or jamming during the course of transportation.
In order to overcome the disadvantages as described above, there has been proposed, for example, in Japanese Patent publication Tokkaisho 101538/76, another electrophotographic copying apparatus provided with a mechanism for copying thick originals and another mechanism exclusively for copying sheet originals. In this prior art copying apparatus, when thick originals are to be copied, the original is placed on an original platform and scanned by first and second carriages moving at a speed ratio of 1:1/2, while for copying sheet originals, the sheet original is transported along a transporting path for the sheet original at the upper part of a scanning starting position of said first carriage with the carriages being held stationary so that light images of the sheet original being transported during scanning are projected onto the photosensitive member through the stationary first and second carriages. More specifically, the construction of such a known copying apparatus is shown in FIG. 1, in which, below a transparent platform P for supporting a thick original (not shown), there is disposed an optical system O which includes an illuminating lamp I and a first reflecting mirror M1 moved horizontally for scanning in a direction parallel to the platform P at a speed V equal to the circumferential speed of a photoreceptor drum D, a second and third reflecting mirrors M2 and M3 also moved horizontally at half the circumferential speed of the photoreceptor drum D, and a fourth reflecting mirror M4 and an image forming lens assembly L which are stationary. The starting positions of the first, second and third mirrors M1, M2 and M3 at the start of scanning are positions shifted to a predetermined slight extent from one end of the platform P in a direction opposite to the scanning direction, taking into account the time for the illuminating lamp I to reach peak intensity of light emission and vibrations of the mirrors M1 to M3 at the time of starting. For copying of sheet originals, a sheet original is transported by juxtaposed transportation rollers (not shown) disposed above the first reflecting mirror M1 while the mirrors M1-M3 are held stationary in the full line positions in the drawing for sequentially directing the light images of the original onto the surface of the photoreceptor drum D for exposure.
The known copying apparatus as described above still has disadvantages in that due to the close proximity of the first and second reflecting mirrors M1 and M2 at the start of the scanning by the optical system O, the part M2a of the second mirror M2 undesirably encroaches upon the light path between the sheet original and the first mirror M1, thus resulting in an obstacle to the exposure. Moreover, in a copying apparatus of the above described type wherein reflecting mirrors such as the mirrors M1, M2 and M3 are reciprocated for the scanning, it is the general practice to provide looseness or side play for reducing friction between sliding members (not shown) holding the mirrors M1, M2 and M3 and guide shafts (not shown) to guide such sliding members for increasing the return speed during reciprocation with improved smoothness. When the optical system O is located at the scanning starting position, however, there is the inconvenience, for example, that the sliding member contacts a damper for restricting the movement of the first mirror at the scanning starting position, with consequent inclination of the first mirror M1 due to the presence of the side play as described above, and if the surface of the photoreceptor drum D is exposed to the light images during transportation of the sheet original, while the optical system O is held stationary at the scanning starting position, a true image is not formed on the surface of the photoreceptor drum D due to the inclination of the first mirror M1, resulting in distortion of the copied image.
Accordingly, an essential object of the present invention is to provide an electrophotographic copying apparatus which is free from the foregoing disadvantages especially during copying of sheet originals so as to provide clear and accurate copied images having no distortion.
Another important object of the present invention is to provide an electrophotographic copying apparatus of the above described type which is capable of positively transporting sheet originals without wrinkling or jamming with substantial elimination of disadvantages inherent in the conventional copying apparatus of this kind.
A further object of the present invention is to provide an electrophotographic copying apparatus of the above described type which has a simple construction and is compact in size, and can be readily put into production at low cost.
In order to accomplish these and other objects, according to one preferred embodiment of the present invention, the electrophotographic copying apparatus includes means for transporting sheet originals having transporting rollers and disposed adjacent to a transparent platform for thick original at the upper portion of the copying apparatus, and means for moving an image forming optical system, at the time of change-over from copying thick originals to copying sheet originals, from a scanning starting position for thick original copying to a stationary position of the optical system for sheet original copying in order to eliminate the inconveniences inherent in exposures in the conventional copying apparatuses during copying of sheet originals, while the distance between the first reflecting mirror and second reflecting mirror at the scanning starting position is reduced for making the size of the copying apparatus itself compact. Moreover, the transportation rollers for the originals are provided above and below the path of the sheet originals for positive transportation of such sheet originals without wrinkling and jamming.